(1) Field of the Invention
The present invention relates to infrared transparent glass ceramic articles, and in particular, to such glass ceramic articles useful for top plates of cooking stoves and to a production method thereof.
(2) Description of the Prior Art
It is known in the prior art to use a crystallization glass for top plates of cooking stoves.
U.S. Pat. No. 4,211,820 by Cantaloupe et al discloses such a glass ceramic sheet useful as surfaces for smoothtop cooking stoves which consists essentially, by weight, of 2.5-4.5% Li.sub.2 O, 1-2% MgO, 1-2% ZnO, 19.5-21% Al.sub.2 O.sub.3, 66.5-68% SiO.sub.2, 4-5% TiO.sub.2, and 0.02-0.2% V.sub.2 O.sub.5, the total of these ingredients being 98% or more.
The glass ceramic sheet, in thickness of about 5mm, will display a warm brown coloration and a transmittance of about 20-60% when measured at 800nm.
The glass ceramic sheet is also characterized by a surface layer containing .beta.-quartz solid solution crystals and an interior containing .beta.-spodumene solid solution crystals dispersed within a glassy matrix. The development of these two crystals improves the mechanical strength of the sheet, because the former has a thermal expansion coefficient lower than that of the latter to thereby cause surface reinforcement of the sheet.
However, the development of .beta.-spodumene solid solution crystals tend to unadvantageously cloud the ceramic article white. The white clouded glass ceramic sheet has a problem in appearance and has a reduced infrared transmittance so that a heating element of a cooking stove cannot be observed through the glass ceramic sheet. Therefore, the use of the ceramic sheet for cooking stoves may be unsafe for operators of the stoves.